Card attenuators are old and well known, see U.S. Patents:
U.s. pat. No. 3,521,201, Veteran, July 21, 1970 PA1 U.s. pat. No. 3,260,971, Bacher et al., July 12, 1966 PA1 U.s. pat. No. 3,227,975, Hewlett et al., Jan. 4, 1966 PA1 U.s. pat. No. 3,157,846, Weinschel, Nov. 17, 1964
It is also desirable to have attenuators in which any of a wide range of attenuation values may be selected and, therefore, drum-type attenuators have been developed, see U.S. Pat. No. 3,157,846. See also U.S. Pat. No. 3,805,209, to Keranan, issued Apr. 16, 1974.
The prior attenuators are expensive to construct. For example, in connection with the aforesaid U.S. Pat. Nos. 3,157,846 and 3,227,975, the characteristic impedance is determined by the shape and dimensions of the cross-sections of the inner and outer conductors, as well as by the dimensions and dielectric constant of the card. Therefore, it is necessary to employ close fabrication tolerances in the construction of all of the aforesaid parts of those attenuators. In addition, it is necessary that the outer conductor must provide full shielding to the outside world, especially for the higher dB values of attenuation, must have a shape as required for the desired characteristic impedance, and must provide a high conductive connection to the resistive film on the card. Hence, manufacture of the outer conductor is quite expensive. Indeed, it is customary to use machined metal parts for the outer conductor as well as for many other parts of the attenuator.
Furthermore, when it is desired to have a step or drum attenuator, that is one which is adjustable to different values of attenuation, many problems arise because it is not only necessary to provide accurate tolerances to all parts when the attenuator is first constructed, but it is necessary that the design be such that the relation of the various parts of the attenuator be accurately maintained throughout the life of the attenuator.
A main object of the invention is to provide a card-type attenuator which overcomes the aforesaid disadvantages.
Another object is to provide a card-type attenuator that may be incorporated in a step or drum type device and which will maintain its accuracy notwithstanding the forces arising from time to time due to switching from one degree of attenuation to another. Still other objects relate to providing improved cards for card-type attenuators.
A further object of the invention is the provision of an attenuator with a reduced requirement for machined parts.
An important object of the invention is to provide a low cost broadband attenuator.
Other objects and advantages of this invention will appear as this description proceeds.